Imidazole derivatives are known which have a wide spectrum of antimicrobial activity both in vitro and in vivo and which can be used topically in the treatment of skin diseases such as dermatophytosis, cutaneous candidosis, onychomycosis, tinea capitis and pityrosporosis. In addition, they can be used topically in the treatment of seborrheic dermatitis, pityriasis capitis and pityriasis versicolor which all involve the yeast Malassezia furfur. 
One such imidazole derivative, ketoconazole, was originally described in U.S. Pat. No. 4,335,125 in which its principal utility was given as an antifungal compound. Ketoconazole is also disclosed in U.S. Pat. No. 4,569,935 to be useful in the topical treatment of psoriasis and seborrheic dermatitis.
U.S. Pat. No. 4,298,604 describes topical compositions containing the corticosteroid betamethasone dipropionate and, as a fungicidally active agent, clotrimazole.
Ketoconazole, however, has very poor solubility characteristics in common solvents such as water and alcohols. For topical use it is only available commercially at a concentration of 2 wt % in suspension in a semi-solid aqueous cream and in a shampoo for application to the scalp.
Both of these commercial formulations have disadvantages. The cream provides poor bioavailability of ketoconazole as the discrete particles thereof do not permeate very efficiently into the skin. In addition, the cream is not suitable for application to the hair bearing areas of the body, particularly the scalp. The cream is difficult to apply and localise over the affected area and is also cosmetically unacceptable if left on the skin for any length of time as it leaves a greasy deposit.
The shampoo is designed to be left on the scalp for only very short periods which therefore does not provide the extended contact time necessary to maintain a therapeutically adequate concentration on the scalp. It is also difficult to get the active drug to the scalp if the shampoo is not massaged in correctly. Furthermore shampoos tend to contain anionic surfactants which may hinder the drug permeating through the skin and may also irritate the skin.
There is therefore a need for a composition comprising a suitable concentration of ketoconazole for direct application to the skin in order to treat susceptible infective conditions, which can be used on skin bearing hair such as the scalp, and which has cosmetically acceptable characteristics and good permeability through the skin.
Desirably such a product should be a true evaporative solution of low viscosity and once applied it should leave a relatively small liquid residue.